This application claims priority of DE 198 57 744.3, filed Dec. 15, 1998, the disclosure of which is expressly incorporated by reference herein.
The present invention relates to a press for massive forming.
In the case of a fairly large number of presses, the lower dead center position, in which the upper tool part and the lower tool part of the forming tool take up their maximally approached position, must be adjustable. This requires corresponding adjusting devices on the press plunger if the adjustment is not to take place at the tools. As a rule, adjustable tools require much higher expenditures than non-adjustable tools.
Particularly in the case of presses for massive forming, considerable forming forces occur on the workpieces which must be applied by the slide. An adjusting device must therefore be capable of withstanding the occurring forces, i.e., that is, it must have a correspondingly robust construction. If an adjusting device is provided on the press slide, it will be moved back and forth with the slide. Particularly at higher stroke rates, the weight of the adjusting device will therefore be noticeable. The weight should therefore be kept as low as possible.
As a rule, the adjustment of the lower dead center of a press is necessary after a tool change. Beyond that, a readjusting of the lower dead center may become necessary not only when the press is set up but occasionally, also at other points in time. This should naturally take place as easily as possible. Stoppage times should be minimized.
An object of the present invention is to provide a press, particularly for massive forming, which can be easily operated with a view to the above-mentioned requirements.
This object has been achieved by providing a press for massive forming and the like having a press plunger arranged is to be driven back and forth by a drive in a working direction and in an opposite direction and having an adjustably disposed pressure piece, an adjusting device for supporting the pressure piece on the press plunger at least in the working direction in adjustable positions, an adjusting drive operatively associated with the adjusting device for position influencing, a holding device configured to hold the pressure piece at least in the operation on the adjusting drive and a control device for controlling the adjusting drive.
The press has a press plunger with an adjustable section. The adjustable section is a pressure piece which operates directly as the tool or which carries a tool. At least when the press is operating, the pressure piece is fixedly connected with the rest of the press plunger. It is locked to the latter and, together therewith, carries out a back-and-forth working movement in the working direction and in the opposite direction.
The adjustment of the pressure piece with respect to the rest of the press plunger is carried out by an adjusting device. The adjusting device is primarily used for supporting the pressure piece in an adjustable position on the remaining press plunger.
An object of the adjusting device is, therefore, to transmit, in the adjusted relative position between the pressure piece and the rest of the press plunger, the required pressure force from the press plunger to the pressure piece.
The upward movement of the plunger is transmitted by the holding device to the pressure piece. The holding device can be a tensioning device which tensions the pressure piece against the adjusting device and holds it on the latter only when a desired pressure piece working position is set.
The function of the tensioning device is preferably only that of locking the pressure piece. When the adjusting device takes over the force transmission for the working stroke, the tensioning device only still has to transmit the withdrawal force from the press plunger to the pressure piece during the return stroke. Because the forces occurring in this case are clearly lower than the forming forces, the tensioning device may have a comparatively light construction. The mechanism used for adjusting the pressure piece is therefore divided into an adjusting device and a tensioning device.
The tensioning device can be automatically released and locked by a tensioning drive so that the adjusting device can be adjusted load-free at low expenditures of force as soon as the tensioning device is released. No manual access is required in this case to the pressure piece or its tensioning device. The pressure piece adjustment can be carried out fully automatically or at least in a remote-controlled manner by the adjusting drive and the tensioning drive. This is particularly advantageous and important in the case of presses which have a working space for the tool and the plunger which is separate from the environment. As a result, the adjusting operations can be carried out more easily and faster and with lower physical effort. Without the requirement of opening covers, protective grids or the like, the tensioning device can be released very rapidly, whereby a construction is obtained which is reasonable in cost.
In principle, the adjusting device can be implemented in different manners. It was found to be advantageous, however, to provide an intermediate piece between the slide and the plunger whose effective length can be adjusted by the adjusting drive. The intermediate piece may be, for example, a straight wedge or a worm, i.e., a spirally wound wedge, whose wedge surface extends in a circle and ascends in the axial direction. An intermediate piece which is a straight wedge is displaced transversely to the plunger for the adjustment of the plunger, for which a linear drive is preferably used. This linear drive may be formed, for example, by a hydraulic motor or an electric motor with a geared spindle drive. Other drives are contemplated as being within the scope of the present invention.
The preference of the construction of the adjusting device as a straight or curved or spiral wedge advantageously results in a self-locking arrangement if the wedge angle is sufficiently acute. For example, a displacement or rotation of the wedge because of the forming forces to be transmitted does not have to be expected if the static friction between the inclined surface of the wedge and the corresponding opposite contact surface is greater than the force component in the surface direction resulting from the force transmission and the inclination of the surface.
In addition, the movement of the wedge can be limited by a self-locking linear drive. Such a drive is obtained, for example, by the above-mentioned geared spindle drive. Also, worm gears or other self-locking gears may be arranged in the force transmission path. As required, the adjusting drive can also be braked electrically or mechanically.
The tensioning device tensions the pressure member against the adjusting device. In a particularly simple embodiment, a screw cap is used as the tensioning device and holds the plunger against the adjusting device. The screw cap is connected with a tensioning drive, such as a hydraulic motor or an electric motor. When the tensioning device is released, the adjusting device can be adjusted with a low expenditure of force. When the tensioning device is in the tensioning position, the adjusting device is locked thereby and can preferably not be adjusted. This minimizes the danger of an accidental release as the result of the adjustment of the adjusting device. In addition, the adjusting drive can be triggered by low power.
In a currently preferred embodiment, the pressure member is displaceably disposed in a receiving sleeve which is detachably connected with the press slide. The receiving sleeve can, for example, be held by tensioning claws which are to be pushed laterally onto inclined surfaces. The force transmission from the slide onto the pressure piece does not take place, however, by way of the receiving sleeve but preferably from the press slide by way of the adjusting device directly to the pressure piece. In this manner, elastic microdeformations, which may occur on the pressure piece and the slide in the proximity of the lower dead center at maximal forming force, are kept away from the receiving sleeve. The tensioning claws are prevented thereby from increasing their tension and tightening on the inclined surfaces of the receiving sleeve when the press is operating. This results in a detachability and exchangeability of the receiving sleeve together with the pressure piece which presents no problems.
In a preferred embodiment, the control device coordinates the operation of the adjusting drive and of the tensioning drive. The adjusting drive is not activated before the tensioning drive has released the tensioning device. In addition, the tensioning drive does not lock the pressure piece, i.e., tensions it against the adjusting device, before the adjusting drive is stopped.
In a comfortable embodiment, particularly during the adjustment of the pressure piece away form the press slide, (i.e., during the adjustment in the working direction), the control device can open the tensioning sufficiently wide to create the required clearance for the resetting of the adjusting device. In order to achieve this, the adjusting drive and the tensioning drive can be constructed as servo motors. The number of revolutions required for causing a desired adjustment can be precalculated and defined by the control device.
The holding device can also be operated without a tensioning device. The adjusting device, which is constructed, for example, as a wedge which can be adjusted transversely to the working direction, is then constantly connected with the press plunger and with the pressure piece. For the connecting, linear guides can be used whose moving direction coincides with the moving direction of the wedge.